In our prior application, Ser. No. 431,705, now U.S. Pat. No. 3,880,633 was disclosed a method of coating a glass sheet with a thin film of SnO.sub.x, in a continuous process, the glass moving continuously in a bath of molten material, and a spray containing a tin compound being applied in successive transverse passes of the glass. The glass moves in a bath of molten material which may be tin, but may also be a salt, capable of sustaining the glass or partially sustaining the glass. In the latter case further support is supplied for the glass, so that its upper surface remains exposed, while at least its under surface is immersed. The contents of Ser. No. 431,705 are incorporated herein by reference.
It is known to coat glass with SnO.sub.x, and it is also known that if glass is coated with SnO.sub.x, the SnO.sub.x being transparent and electrically conducting, the coating will serve to reflect infra-red energy while passing visible light, so that heating energy applied internally of a heated enclosure, employing one or more panes of such coated glass, is conserved internally of the enclosure since radiation of infra-red energy outwardly of the structure through the glass is reduced. It is an object of the present invention to improve such coatings in such manner as to increase infra-red reflectivity of the SnO.sub.x coating, while maintaining good transmission in the visible spectrum. The increase is a function of the reduced resistivity of the film, which is about 8-17 ohms per square, transmissibility of visible light being about 80%. Conventional coatings have resistivities of about 50-90 ohms per square and transmissibilities of about 70-78%. As .OMEGA./sq. is reduced transmissibility of visible light is not radically reduced but a large increase of infra-red reflectivity occurs.